Electric conduction through supramolecular assemblies of triarylamines

ABSTRACT

A method is provided for modifying a surface of a solid conducting material, which includes applying a potential difference between this surface and a surface of another conducting solid material positioned facing it, and wherein, simultaneously, the surface (S) is put into contact with a liquid medium comprising in solution triarylamines (I): 
                         
while subjecting these triarylamines (I) to electromagnetic radiation, at least partly converting them at into triarylammonium radicals. Also provided is a conducting device which includes two conducting metal materials, the surfaces of which, (S) and (S′) respectively, are electrically interconnected through an organic material comprising conducting fibrillar organic supramolecular species comprising an association of triarylamines of formula (I).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.13/284,104, filed Oct. 28, 2011, which claims benefit of U.S.Provisional Application No. 61/418,645, filed Dec. 1, 2010, and acontinuation of International Application No. PCT/FR2011/052529, filedOct. 28, 2011, which are all incorporated by reference.

The present invention relates to the field of electric connection ofconducting solid elements separated from each other by small distances,typically of the order of a few tens to a few hundred nanometers, forexample conducting solid elements of the type of those applied inelectronic and optoelectronic devices, such as light emitting diodes(LEDs and OLEDs), field effect transistors (FETs and OFETs) andphotovoltaic devices such as solar cells. The invention according to aparticular aspect for example relates to the manufacturing or repairingof electronic circuits (notably printed circuits) where an electricconnection has to be established between components for example afterhaving been broken.

To this day, in order to make an electric connection of theaforementioned type, between conducting solid elements separated bysmall distances, various methods have been proposed which generallyprove to be unsatisfactory or limited.

Thus, deposition of metal powders between the conductors to be connectedhas for example been contemplated. The use of a metal powder of thistype generally leads to an electric connection, but generally proves tobe relatively difficult to localize accurately, which may lead toundesired connections between other electric conductors than those whichare desirably interconnected. Further, the efficiency of the electricconnection obtained with a metal powder often proves to be rather poor.Indeed, schematically, powders lead to point-like contacts with theconductors to be connected, which does not induce an optimum electricconnection. More generally, the use of metals for making electronicdevices generally requires complicated and/or expensive shaping stepsand generally leads to rigid devices.

Alternatively, for manufacturing electronic devices, the use ofconducting polymers has been proposed, which are typically depositedbetween conductors to be connected within a solvent which is thenevaporated. Some of the proposed polymers within this scope prove to berelatively interesting for connecting specific metal conductor elements,notably insofar that with them it is possible to obtain more flexibledevices than those obtained with metals, and with generally lower costs.However, there again, when it is desired to connect two conductingsolids with a polymer, it is often difficult to confine the deposit ofthis polymer to a well-delimited area. Further, when a conductingpolymer leads to interesting results with a given metal conductor, theseresults cannot be generally transposed to other metal conductors.Indeed, the efficiency of the electric connection made with an organicconducting polymer most often depends on the adequacy of the valencebands and adsorption bands of the polymer and of the metal conductor towhich it is connected.

Further, organic conducting polymers have the drawback of having abehavior of non-ohmic conductors. Another negative aspect related to theuse of conducting organic polymers is that they often contain metal ionsas dopants, which may have a non negligible impact in terms of toxicityand of detrimental repercussions on the environment, which is anobstacle to their use on an industrial scale.

Another possibility for connecting two electrodes by means of an organicconductor is to accurately deposit metal carbon nanotubes. This actuallyhas very low interface resistances and an ohmic behavior with metal typeconduction. However, the difficulty in insulating and positioning thesenanotubes on metal contacts again makes this method difficult to applyand with a high cost.

An object of the present invention is to provide a method which i.a.allows electric connection of two conducting solid elements, in anaccurate, simple, repeatable and efficient way, and this preferably byavoiding the drawbacks of the aforementioned methods, notably byensuring between both conductors an efficient conduction of the ohmictype.

For this purpose, the present invention proposes a novel method, whichgives access to the deposition of conducting organic fibrillarstructures at the surface (S) of a solid conducting material, whichallows i.a. the connection of this thereby modified surface (S) with asurface (S′) of another conducting solid placed facing the surfacebearing the fibrillar structures, when this other surface (S′) is at asufficiently small distance so that the fibrillar structures may form aconnection between both surfaces (S) and (S′) facing each other.

More specifically, according to a first aspect, the object of thepresent invention is a method for modifying a surface (S) of a solidconducting material which comprises a step (E) in which a generallynegative potential difference is applied between said surface (S) and asurface (S′) of another conducting solid material positioned facing saidsurface (S), simultaneously with the contacting of said surface (S) witha liquid medium comprising in solution triarylamines fitting the formula(I) hereafter:

wherein:

-   -   each of the groups -A¹- and -A²-, either identical or different        (and preferably identical), designates a simple covalent bond or        else a group —O— or —S—, —NH—, NH(C═O), or —NR³—, and preferably        a group —O—;    -   each of the groups R¹, R² and R³, either identical or different        (R¹ and R² being preferably identical), represents:        -   an aromatic group, preferably a benzyl group; or        -   a (preferably linear) hydrocarbon chain comprising from 4 to            30, for example 5 to 20 carbon atoms, preferably an            advantageously linear fatty chain, notably an alkyl group;            or        -   a polyethylene glycol chain; and    -   R is a terminating group, which preferably is a linear or        branched hydrocarbon chain, advantageously comprising from 1 to        10 carbon atoms, optionally halogenated and optionally        interrupted with one or several heteroatoms selected from N, O        or S,    -   R more preferably being an alkyl group, optionally halogenated,        preferably comprising from 1 to 8 carbon atoms,        while subjecting the triarylamines (1) to electromagnetic        radiation or to chemical or electrochemical oxidation, suitable        for converting them at least partly into triarylammonium        radicals, this irradiation may typically be achieved with        sunlight in a chlorinated solvent (dichloromethane, chloroform,        tetrachloroethane, dichlorobenzene, etc).

With the work which was carried out by the inventors within the scope ofthe present invention, it was now possible to show that the applicationof step (E) as defined above gives the possibility of obtaining in anextremely simple and rapid way, a deposit of conducting organic species,with a fibrillar shape (i.e. globally having the morphology of a smallfiber), and immobilized on the surface (S) of the solid conductingmaterial. These conducting fibrillar organic species, objects of theinvention, consist of a supramolecular association of triarylamines offormula (I) of the type of associations which were described in solutionby the inventors in Angew. Chem. Int. Ed., Vol. 49, pp. 6974-6978 (2010)which is incorporated herein by reference, these fibrillarsupramolecular species being according to the present inventionspecifically grafted on the surface (S) of the solid conducting materialat the end of step (E).

The present invention according to a second aspect relates to aconducting material or device comprising two conducting metal materials,the surfaces of which, (S) and (S′) respectively, are electricallyinterconnected by an organic material comprising conducting fibrillarorganic supramolecular species comprising an association oftriarylamines of formula (I).

By “conductors”, reference is made to electric conduction.

By “electrically interconnected” is meant the capability of havingpreferably a conductivity above 10³ S.m⁻¹, and generally from 10⁴ S.m⁻¹to 10⁵ S.m⁻¹. The devices of the invention have current (I) valuesattaining the mA range. The conductance is generally of the order of afew tens of mS. According to a preferred embodiment, the devices of theinvention advantageously have ohmic resistivity.

According to another aspect, the object of the present application is amethod for preparing the aforementioned supramolecular species. Thismethod includes a step in which a liquid medium containing triarylaminesof formula (I) is subjected to electromagnetic radiation (typicallysolar radiation) or further to chemical or electrochemical oxidation,suitable for at least partly converting them into triarylammoniumradicals, while subjecting them to an electric field typically from 200to 600 mV, for example between 250 and 500 mV.

According to the method of the present invention, these fibrillarsupramolecular species are specifically grafted onto surface (S) of thesolid conducting material at the end of step (E). These supramolecularspecies typically have the shape of small fibers having a length of theorder of 10 nm to 1,000 nm, notably between 50 and 1,000 nm and adiameter from 5 to 50 nm, for example from 10 to 50 nm. Considering theapplication of a potential difference between the surfaces (S) and (S′)during step (E), these fibers are formed in a localized way between bothsurfaces and parallel to the electric field lines. Moreover, they aresystematically grafted on the surface (S), which allows suppression ofthe formation of free fibrillar supramolecular species (i.e.non-bridging between the electrodes) after rinsing. Thus with thismethod, unlike present techniques, it is possible to achieve anextremely localized deposit of conducting organic compounds, exclusivelyin the area located between both surfaces. Unexpectedly, considering thetechniques existing to this day for achieving this type of deposition,this accurate localization is further achieved directly without havingto apply expensive or complicated means. Thus, generally, step (E) in asimple, efficient and inexpensive way (simply by introducing thecompounds of formula (I) in solution between both surfaces (S) and (S′),by applying a simple potential difference between both of these surfacesand by subjecting the assembly to irradiation, typically with sunlight)gives the possibility of grafting organic fibrillar structures withelectric conduction at the surface of a conducting solid.

According to a particularly interesting embodiment, step (E) isconducted with a sufficiently small distance between the surfaces (S)and (S′) so that the fibrillar supramolecular associations formed on thesurface (S) come into contact with the surface (S′). In this case, step(E) leads to an electric connection of the conducting surfaces (S) and(S′). Typically, in this case, the surfaces (S) and (S′) facing eachother are separated by 1 micron or less, or, at the very least, thereexists at least one area of the surface (S) at a distance of 1 micron orless (for example from 10 to 1,000 nm) from an area of the surface (S′).Preferentially, when an electric connection of the surfaces (S) and (S′)is sought, the latter are parallel or substantially parallel with a gapbetween both surfaces ranging preferably from 10 to 1,000 nm, forexample from 50 to 500 nm.

According to a particular embodiment, said conducting material or devicehas a metal/organic interface and the surfaces (S) and (S′) areseparated by a distance of 10 to 500 nm, and preferably from 50 to 200nm, in which said organic material comprising fibrillar organicsupramolecular species fills the distance separating the surfaces (S)and (S′) of both metal materials. Said distance is typically 80±20 nm.This is referred to as a <<nano-gap>>.

According to an alternative, the material or device of the invention hasa length of the surfaces (S) and (S′) facing each other comprisedbetween 10 μm and 1,000 μm, and preferably from 50 to 500 μm. Saidlength is typically about 100 μm.

According to a preferred alternative, the fibrillar organicsupramolecular species are oriented as a parallel bundle of<<nano-wires>> extending radially relatively to the conducting surfaces(S) and (S′), i.e. so that the greatest length of the fibrillar speciesjoins said surfaces (S) and (S′).

Fibrillar organic supramolecular species are preferred, for which thelength corresponds to the distance separating the surfaces (S) and (S′)of both metal materials.

Preferably, the metal materials are metal materials of conductingelectrodes. As a material, preference is given to metals selected fromtransition metals and preferably from gold (Au) nickel, (Ni), titanium(Ti), silver (Ag), iron (Fe), platinum (Pt), copper (Cu), cobalt (Co),zinc (Zn), chromium (Cr), manganese (Mn), or alloys comprising one ormore of these metals. The electrodes may comprise an association of anelectrode comprising or consisting of gold and nickel or of Nickel andiron, or of copper and gold, or of silver and gold, preferably with goldin surface of the electrode.

The present invention further relates to an interface between two metalelectrodes comprising or consisting of fibrillar organic supramolecularspecies of the invention.

The invention also relates to the use of fibrillar organicsupramolecular species comprising triarylamines fitting formula (I) inorder to connect together the surfaces (S) and (S′) of two conductingelectrodes. The electrodes may be the aforementioned metal electrodes.

Preferably, at least one electrode comprises a transition metal, andpreferably the whole of the electrodes used (for example the positiveelectrode and the negative electrode).

According to an alternative, the conducting metal of at least oneelectrode is covered with a gold (Au) deposit. Preferably, the whole ofthe electrodes used comprise a gold deposit (for example the positiveelectrode and the negative electrode).

In the particular case when step (E) is used for making the electricconnection of the surfaces (S) and (S′) according to the specificembodiment described above, this leads, as this is systematically thecase in step (E), to the formation of fibrillar supramolecular speciesin an exclusively localized way within the space comprised between bothsurfaces, without any risk of depositing conducting organic compounds inother areas. The method consequently proves to be particularly selectiveand targeted, unlike most techniques applying organic compounds forconnecting two conducting elements. Further, the fibrillarsupramolecular species which are formed, are oriented by themselvesparallel to the lines of the applied electric field between the surfaces(S) and (S′), i.e. along a parallel bundle of <<nano-wires>> extendingradially relatively to the conducting surfaces (S) and (S′), which isthe optimum conformation for ensuring maximum electric connectionbetween both surfaces. Further, the connection is effected rapidly, withresponse times at most of the order of one second.

In addition to this particularly favorable conformation, it is furtherfound that unexpectedly, the fibrillar supramolecular species formedduring step (E) are very good conductors, with a conductivity of theorder of that of the best organic conductors known today (typically ofthe order of several tens of kiloSiemens per meter) and further with abehavior of ohmic conductors, unlike most conducting polymers. In otherwords, the supramolecular species schematically behave like metalnano-wires, notably with a resistance which decreases with temperature(notably in the range between 4 and 298 K). In a particularly surprisingway, this effect is obtained within the scope of the present inventionwith species which are purely organic, without requiring application ofadditional metal cations which are conventionally used as dopants inmany conducting organic polymers. With this possibility of doing withoutthe application of metal compounds, it is possible to avoid theassociated drawbacks in terms of toxicity and repercussion on theenvironment, which further is a particularly interesting aspect of themethod of the invention.

Further, in still a more unexpected way, the inventors have brought tolight within the scope of the present invention that the fibrillarsupramolecular species which are produced in step (E), lead toparticularly low contact resistances at the contact with the surfaces(S) and (S′). Indeed, the obtained contact resistance may be as low asof the order of 10⁻² Ω.cm in most of the cases, versus contactresistances which are at the very least of the order of 10 kΩ.cm withmost molecules recommended in the state of the art.

Moreover it should be emphasized that, unlike most organic compoundsused as electric conductors, the fibrillar supramolecular species whichare made in step (E) lead to good results in terms of conductivity,notably when the conducting materials present at the surfaces (S) and(S′) comprises gold. Good results are further generally obtainedregardless of the nature of the conducting material present at thesurfaces (S) and (S′), which allows the method to be particularlymodular.

Thus, it is found that step (E) in an extremely simple and direct wayallows an efficient electric connection to be made between conductingobjects separated from each other by a few tens to a few hundrednanometers, and this regardless of their exact physico-chemical nature.Unexpectedly, this particularly effective electric connection isobtained by simple self-association of the compounds of formula (I)during step (E), without having to apply complicated or expensivetechniques. The fibrillar supramolecular species made in step (E)consequently are an extremely interesting alternative to organiccompounds such as oriented conjugate polymers which are by far much morecomplicated to synthesize.

In addition to these different advantages, the inventors have furthershown within the scope of the present invention that the fibrillarsupramolecular species deposited on the surface (S) are stable at roomtemperature and they are even more stable, including at a highertemperature, once the solvent used in step (E) has been removed forforming these species. Consequently, most often in the method of theinvention, step (E) is followed by a step (E′) for removing the solventused in step (E), which may typically be achieved by simple rinsing. Byapplying this step (E′), it is possible to stabilize the fibrillarsupramolecular species attached on the surfaces (S) and optionally (S′),these species generally remaining stable and secured to the surface (S),and to the surface (S′) if required, even when they are brought totemperatures of the order of 100° C. With this step (E′), it is alsopossible to remove possible compounds which are not engaged in theformation of the supramolecular species bound to the surface (S).

It should be noted that in the presence of a solvent, on the contrary,the fibrillar supramolecular species tend to disassemble at a hightemperature, in particular at a temperature in the order of 100° C., inorder to lead to the formation of a solution comprising the compounds(I) in a solubilized form. This specificity makes the formation of thefibrillar supramolecular species of step (E) reversible. Thus, if needbe, an electric connection as obtained at the end of step (E) may verysimply be broken by bringing the medium to a temperature of the order of100° C., if the solvent has not been removed. With this possibility itis for example possible to correct possible connection errors during themanufacturing of electric or electronic circuits. If step (E′) has beenapplied, it is still possible to consider such a reversibility. In orderto disassemble the fibrillar supramolecular species, it is thensufficient to put these species back in the presence of a solvent, andthen to raise the temperature of the medium to 100° C. The reversibilityof the method further is one of its numerous assets, making it mostparticularly suitable for an industrial application. This reversibilityof the formation of the fibrillar supramolecular species from compoundsof formula (I) allows them to be considered for making memories.

Different advantages, features, and preferential embodiments of theinvention will now be described in more detail.

Triarylamines of Formula (I)

Preferably, the triarylamines of formula (I) used in step (E) are apopulation of identical molecules. However, according to certainembodiments, the use of a mixture of several distinct triarylamines isnot excluded.

According to an embodiment well adapted to the application of thepresent invention, the triarylamines of formula (I) used in step (E) arecompounds wherein each of the groups -A¹- and -A²- is a group —O—.

Moreover, it proves to be generally of interest that in thetriarylamines of formula (I) used in step (E), each of the groups R¹ andR² independently represents:

-   -   a benzyl group; or    -   an advantageously linear alkyl group typically comprising from 6        to 18 carbon atoms, preferably from 7 to 10 carbon atoms.

Thus, according to an interesting embodiment, the triarylamines offormula (I) used in step (E) may for example fit the formula (1a) below:

wherein:

-   -   each of the groups R¹ and R², either identical or different (and        preferably identical) have one of the aforementioned meanings        and preferably designates a benzyl group or else an        advantageously linear alkyl group, comprising from 6 to 18, for        example 7 to 10, and notably 8 carbon atoms;    -   A is a hydrogen group —H; a halogen group, for example a group        —Cl; or else an alkyl group typically comprising from 1 to 8        carbon atoms (for example, 5, 6, or 7 carbon atoms).

Triarylamines adapted to the application of the invention notablyinclude, in a non-limiting way, the compounds fitting formula (Ia)above, wherein R¹, R^(2,) and A have one of the following meanings:

-   -   R¹=R²=C₈H₁₇ (linear) and A=Cl; or    -   R¹=R²=C₈H₁₇ (linear) and A=H; or    -   R¹=R²=C₈H₁₇ (linear) and A=C₆H₁₃; or    -   R¹=R²=benzyl and A=H; or    -   R¹=R²=benzyl and A=Cl.

A method for preparing these compounds was notably described in Angew.Chem. Int. Ed., Vol. 49, pp. 6974-6978 (2010).

Regardless of the exact nature of the triarylamines applied in step (E),the latter are applied within a solvent. This solvent may be selectedfrom all the solvents capable of solubilizing the compounds of formula(I) used in step (E). Well-adapted solvents within this scope arechlorinated solvents, such as chloroform, dichloromethane or furtherstill 1,1,2,2-tetrachloroethane.

The step.(E′) for removing this solvent may typically be carried out byusing one of these same chlorinated solvents as a rinsing solvent.

Triarylamines are generally applied in step (E) as solutions havingconcentrations of the order of 1 to 100 mmol/L, preferably between 5 and20 mmol/L. Such solutions are liquid compositions at room temperatureand clearly less viscous than the usual compositions of conductingorganic polymers known from the state of the art, this low viscosityallowing improvement in the control and handling as compared with themethods using this type of polymers, this further is a non-negligibleadvantage of the method of the invention.

The Potential Difference Applied in Step (E)

In the method of the invention, a potential difference is appliedbetween the surface (S) and the surface (S′), so as to induce anelectric field in the space located between both of these surfaces.Generally, this potential difference is negative, so as to inducegrafting of the fibrillar supramolecular species at least on the surface(S).

The absolute value of this potential difference should be sufficient inorder to induce the sought effect, but however it should not be too highso as not to lead to too low conductivities. The value of the potentialdifference should moreover be adapted to the distance between thesurfaces (S) and (S′). As an indication, for a distance between thesurfaces (S) and (S′) of the order of 80 to 100 nm, for example theabsolute value of the potential difference applied during step (E)between the surfaces (S) and (S′) is preferably of the order of 10 to700 mV, more preferentially from 50 to 500 mV, for example between 100and 400 mV, notably between 200 and 400 mV.

For the same gap between the surfaces (S) and (S′), in the particularcase of the use of the compounds of the aforementioned formula (Ia), andmost particularly in the case of the compound of formula (Ia) whereinR¹═R²═C₈H₁₇ and A=Cl, the absolute value of the potential differenceapplied during step (E) between the surfaces (S) and (S′) is preferablycomprised between 250 and 350 mV, typically of the order of 300 mV.

Establishment of the potential difference may be accomplished accordingto any means known per se, the simplest being to connect the surfaces(S) and (S′) to the terminals of an electric generator delivering thesought voltage.

According to an alternative, application of the potential differencebegins before putting the surfaces (S) and (S′) of the solid conductingmaterials in contact with the solution comprising the triarylamines.According to another alternative, application of the potentialdifference begins after this contacting. According to anotheralternative, application of the potential difference begins at themoment of this contacting.

According to a preferred alternative, an initial potential difference ofat least 0.1V and preferably of at least 0.3V is applied between theelectrodes, after light irradiation.

The Electromagnetic Radiation Applied in Step (E)

During step (E), the compounds of formula (I) are subject to irradiationby electromagnetic radiation capable of activating them, i.e. at leastpartly converting them into triaryalammonium radicals.

The radiation used for this purpose contains at least wavelengths withan energy with which the sought conversion may be achieved. For a givencompound of formula (I), this wavelength is very easy to determine sinceit generally corresponds to the absorption peak λ_(max) of the compoundon a UV-visible light absorption spectrum.

For example, for the compound of formula (Ia) wherein R¹═R²═C₈H₁₇ andA=Cl, the effective wavelength is located around 350-365 nm.

Generally, the useful wavelength for activating a given compound offormula (I) is part of the spectrum of sunlight. Consequently, theirradiation of step (E) may advantageously be carried out according to aparticular embodiment by subjecting the medium of step (E) to solarradiation. This particularly simple and inexpensive embodiment makes themethod very easy to carry out.

Alternatively, step (E) may be conducted by using only one portion ofthe solar spectrum. In this case the wavelengths used advantageouslycomprise at least the wavelengths comprised between λ_(max)−25 nm andλ_(max)+25 nm, more preferentially at least the wavelengths comprisedbetween λ_(max)−50 nm and λ_(max)+50 nm.

As regards the irradiation, it should be noted that its power has aneffect on the formation of the fibrillar supramolecular species based oncompounds (I). As a general rule, these species form all the morerapidly as the power is high. Nevertheless, too high irradiation powersshould be avoided since they are capable of leading to parasiticphenomena such as the induction of a radical polymerization reaction. Asan indication, in particular for the aforementioned compounds of formula(Ia), a power of the order of 100 W is suitable (for example between 50and 200 W, i.e. powers of the order of 10 W.cm⁻² based on the distancebut which may be lower and at least as low as 0.01 W.cm⁻² according tothe applied irradiation time), while powers of 1,000 W are detrimentalto the quality of the obtained result.

The irradiation may be replaced with a chemical oxidation step, forexample by using an oxidant such as DDQ (dichlorodicyanoquinone) incatalytic amounts (typically 1%). It is also possible to form radicalswhich are initiators of fibrillar self-assembling, electrochemically byoxidizing the triarylamine derivative.

Regardless of the applied embodiment, conducting the steps (E) and (E′)of the present invention is very simple and inexpensive. In addition tothe aforementioned advantages, it should further be emphasized on thissubject that these steps may advantageously be conducted at roomtemperature.

Because of its ease of application and of its great modularity, themethod of the invention lends itself to a large variety of applications.

In particular, the steps (E) and (E′) may be used for connectingtogether two electric conductors, for example two constituents of anelectronic circuit. Within this scope, the method of the invention maybe used at any scale, including miniaturized or even nanometriccircuits.

A particular application of the method of the invention relates to therepair of electronic circuits interrupted locally. Within the scope, thesteps (E) and (E′) may be used for locally carrying out the equivalentof a “weld” on a damaged portion of the electronic circuit, byreconnecting the interrupted circuit by means of the fibrillarsupramolecular species. In this case, the surfaces (S) and (S′) may forexample be both lips on either side of a break or of a damaged areahaving led to a loss of conduction.

More generally, the method of the invention may be used for anydeposition of fibrillar supramolecular species of the aforementionedtype on a conducting surface, in an organized form, i.e. bound to thesurface and extending radially relatively to this surface.

Within this scope, the relatively rapid response of the system gives thepossibility of contemplating <<writing>> on a conducting surface, bymoving parallel to this surface, a surface (S′) of a smaller size, thissurface (S′) then playing the role of a tip (printing head) defining apattern upon moving over the conducting surface. This embodiment may forexample be used for optically writing conducting tracks based onfibrillar supramolecular species on a conducting support. Suchconducting tracks allow conduction of the metal type while furtherhaving the advantage of being mechanically flexible unlike metal tracks.

According to another aspect, the object of the present invention isconducting materials modified at the surface by fibrillar supramolecularspecies based on triarylamines of formula (I), of the type of thoseobtained at the end of step (E) and of the optional step (E′) definedabove.

Within this scope, the object of the present invention is materialswhich are practically obtained according to steps (E) and optionally(E′) but also all materials having the same characteristics but obtainedaccording to another method leading to the same result.

In particular, the invention encompasses conducting materials which bearat the surface fibrillar supramolecular species based on triarylaminesof formula (I) which are obtained not by using irradiation, but by usingan oxidizing agent in order to induce conversion of the triarylamines offormula (I) into triarylammonium radicals.

The invention also relates to conducting materials which bear at thesurface fibrillar supramolecular species based on triarylamines offormula (I) which are obtained by treating a conducting material via anelectrochemical route in the presence of triarylamines of formula (I).

The materials of the invention may be applied in parallel with aso-called downward moving technique or <<top-down>> approach such asinkjet printing, preferably with a high resolution or a lithographicmethod optionally using patterns induced by light.

The invention also allows applications for welds of electronic orbioelectronic circuits and therefore only relates to such methods.

The present invention and its advantages will still be furtherillustrated considering the example hereafter.

In the figures:

FIG. 1 illustrates a schematic view of the geometry of a nano-gapassociated with a typical conductance measurement and with atomic forcemicroscopy (AFM) images. (A) in particular represents a solution ofcompounds of the invention drop-casted in the dark, on nano-patternedAu/Ni electrodes. The applied potential difference between bothelectrodes is comprised between 0.3 and 0.8V. The measured conductancefor the interconnection without the structures of the invention is ofthe order of one picosiemens. The sample is then subjected to light,which produces radicals inducing the supramolecular structures of theinvention by live radical polymerization resulting in alignedself-assembling along the electric field and strong connection of bothelectrodes. (B): topography of the open gap (on the left) as seen withAFM before irradiation and after irradiation, filled with thesupramolecular structures of the invention (on the right). (C): an AFMimage before radiation showing a nano-gap (surface scale 1500×1500 nm²).(D) an AFM image after irradiation (surface scale 1500×1500 nm²): thenano-gap filled with nano-wires or nano-filaments is seen. (E) Zoom onthe nano-gap filled with nano-wires (surface scale 250×250 nm²).

FIG. 2 represents the ohmic behavior and conductivity characteristics ofthe supramolecular structures versus temperature: (A) current versusvoltage curve, measured at a low temperature (1.5K). (B) normalized R(T)measurement of three devices functionalized by supramolecular structuresof the invention, between room temperature and 1.5K. The initialresistances for each sample at 300K are the following: 22, 45 and 360 Ω.Each sample is correlated by using the equation

${\frac{1}{R}(T)} = {\frac{1}{R_{0}} \cdot {\exp\left( \frac{\hslash\;\omega_{0}}{k_{B}T} \right)}}$wherein k_(B) is Boltzmann's constant andwherein

ω₀ is the energy of the photons.

FIG. 3 illustrates a design of electrodes: (A) a nano-gap of electrodesobserved under a scanning electron microscope (SEM). (B) A zoomillustrating four pseudo-connection points, limiting the seriesresistance of the interconnections to below 2 Ω. (C) A zoom on thenano-gap illustrating a typical distance of less than 100 nm.

FIG. 4 illustrates the current versus voltage I(V) measurements: (A)(IV) of an empty nano-gap (width 100 μm, length 0.08 μm). (B) I(V) of areference nano-gap immersed in a solution of the compounds of theinvention, before light irradiation. The residual current is ascribed toion impurities in the solution. (C) I(V) of a nano-gap afterself-assembly of the compounds of the invention under light irradiation.(D) I(V) of a nano-gap showing the affect of the applied voltage duringthe initial light irradiation (diamonds: 0.01 V, circles 0.1 V, squares:0.3 V).

FIG. 5 represents the differential conductance measured at 200K in vacuoby using the AC bridge technique. (A) reduction of the conductance withthe potential difference indicating possible heating of the samples insolution. (B) an integrated curve illustrating current values of a fewtens of mA at higher potential differences.

EXAMPLE 1

A connection of two electrodes was achieved according to the method ofthe invention, by using a device of the type of the one described inNanotechnology, 21, 335303 (2010), which has two electrodes facing eachother.

To do this, a compound fitting the aforementioned formula (Ia), whereinR¹=R²═C₈H₁₇ (linear) and A=Cl, was used, dissolved in an amount of 10mmol/L in chloroform.

The solution of the compound was placed in the gap between twoelectrodes and then the device was irradiated with white light with apower of 100 W, while imposing a potential difference of 300 mV betweenthe electrodes.

The very rapid formation of an electric connection between bothelectrodes was then observed, which is expressed by a measurement of theconductivity between both electrodes: before the treatment, a current ismeasured of the order of a few picoamperes between both electrodes,versus a current of 0.5 A (i.e. 10⁸ fold increase) after the treatment.

Micrographs reveal the presence of fibrillar supramolecular specieswhich ensure the electric connection between the electrodes, organizedin parallel and extending perpendicularly to the surface of theelectrodes.

EXAMPLE 2

By an optical lithography technique on a silicon substrate, Au and Nielectrodes were made, the surfaces of the electrodes being separated bya distance of about 80±20 nm, over a width of 100 μm. The residualcurrent is less than 1 pA between both surfaces. This circuit isimmersed in a solution of molecules of formula (Ia) and in particular ofmolecules of formula (Ia), wherein R¹=R²=C₈H₁₇ (linear) and A=Cl, in1,1,2,2-tetrachloroethane (C₂H₂Cl₄) (FIG. 1A), in the absence of light.An increase in the current between the electrodes by a few hundred pAwas observed under a differential voltage of a few hundred mV (see FIG.4). Following irradiation, using white light, a six fold increase in thecurrent is observed, thereby attaining values in the mA range. Thecorresponding conductance is of a few tens of mS. These devices with 2terminals with channels and interfaces of series contacts have an ohmicresistive behavior related to high conductivity values as shown by themeasurement of the intensity versus the voltage I(V) (according to FIGS.2A and 4). The conductivity of the channel is estimated as rangingbeyond 10⁴ S.m⁻¹. Alternatively, it is estimated that the interfaceresistance per unit length is equal to or greater than 10⁻⁴ Ω.m. Thisvalue is of the order of six times less than that of the best contactsof simple organic crystals and less than what is obtained with grapheneflakes.

After intense washing of the samples with the solvent, Atomic ForceMicroscopy (AFM) imaging reveals a length of <<nano-wires>> ofconducting organic supramolecular structures exactly in line with thedistance between the electrode surfaces (FIGS. 1B-E), with orientationsalong the electric field applied to the assembly and with a homogeneousdiameter of 12±2 nm. It was discovered that it is important to apply aninitial threshold voltage (of at least 0.1V and preferably at least0.3V?) between the electrodes, before light irradiation, in order toeffectively obtain in a stable way the fibrillar supramolecularstructures.

It was also observed that the method for preparing these structures maybe reversible when the sample is heated for example to 60° C. overnight,since the formed supramolecular structures dissolve. After repeatedassemblings and disassemblings (six times), the metal interconnectionswere not significantly effected by the heating cycles.

After evaporation of the solvent, the obtained structures become stableand provide reproducible results after one night of heating at 100° C.The performances of the samples are not notably sensitive to humiditynor to oxygen which is highly positive for organic electronic devices.It was not necessary to operate under inert atmosphere conditions duringthe preparation of the supramolecular structures. After one month ofstorage, the samples exhibited comparable conducting properties.

Studies versus temperature confirmed that the samples had highconductivity since they systematically and reliably reveal resistivitydecreasing with temperature, down to 1.5K (FIG. 2B). The ohmic profileof the structures was also noted up to high currents at low temperature(FIG. 2A). For the samples exhibiting the smallest resistance, currentsup to 25 mA were observed when they are subject to a potentialdifference of 1V in vacuo (FIG. 4B). The current density is estimated tobe of the order of 10⁷ A.cm⁻², which is remarkably high for organiccompounds and corresponds to electromigration density currents in themetal circuits.

EXAMPLE 3

Samples were also made with analogs of compounds of Example 1. In ablind test configuration, it was noticed that the inter-electrode gapwas only filled with supramolecular structures when they are capable ofself-assembling. This confirms that the conducting properties resultfrom the supramolecular structures of the invention. The followingcompounds were tested.

TABLE 1 Behavior in solution Molécule Determined by ¹H NMR (1) State ofthe gap

1 Self-assembled fermé

2 Self-assembled Closed

3 Self-assembled Closed

4 Non self-assembled Open

5 Non self-assembled Open

6 Non self-assembled Closeda: The gap was however opened after rinsing with solvent underconditions where STANWs derivatives 1-3 remain stable; this shows theweakened mechanical properties of STAWNs starting from compound 6.

With ¹H NMR, it was determined that the compounds 1-3 self-assemble insolutions of CDCI₃ after light stimulation, which is not the case of thecompounds 4-6. This property related to the structure shows that onlythe compounds of the invention have the capability of self-assembling.

The experimentation was carried out by blind tests. The person havingprepared the solutions did not carry out the conductivity measurements.The samples were coded. Each sample was measured under the sameconditions: the 1V potential difference was applied on the solution oftriarylamines 1-6 (1 mg.mL⁻¹), simultaneously with an irradiation of 100W at a constant distance for a period of 10 seconds (≈10 W.cm⁻²); andthen the IN dependency was measured for each distance. The results aresummarized in Table 1. The correlations clearly show that theconductivity is dependent on self-assembly.

Images of the Nano-Gaps.

The morphology and the difference between the electrodes before andafter self-assembly were observed, for this, a scanning electronmicroscope (SEM) was used and an atomic force microscope (AFM) was usedfor obtaining qualitative and quantitative information on the nano-gaps.

The images taken with AFM (FIGS. 1C, D and E) give a specific indicationof the fibrillar structure of the filled nano-gaps.

EXAMPLE 4

Electrodes were made with edge mediated shadow mask lithographyaccording to the technology described in J-F Dayen et al; Nanotrench fornano and microparticle electrical interconnects; Nanotechnology 21335303 (2010)—a triple layer Ti(5 nm)/Ni(35 nm)/Au(20 nm) was firstdeposited by electron beam evaporation, followed by a standard lift-offmethod. The second step comprises the deposition under an angle of 60°,by creating a triple layer Ti(5 nm)/Ni(25 nm)/Au(10 nm) followed by alift-off. The first electrode has a composition related to thesuperposition of two steps, and the second thinner electrode, has acomposition only corresponding to the second layer of the depositedtriple layer (this explains the height difference observed with AFM).The <<nano-gaps>> were made with a fixed inter-electrode distance of 80nm and a length of 100 μm (FIG. 3). After checking the absence of anyresidual current, a solution of the compound formula (Ia), whereinR¹=R²=C₈H₁₇ (linear) and A=Cl (at 1 mg/mL in C²H²Cl⁴), were deposited bydrop casting on the electrodes. A potential difference of more than 0.3Vand up to 0.8V with a DC current, was immediately applied between theelectrodes, the time-dependent change in the current was recorded byusing a measurement instrument with high resistances (electrometers) ofthe Keithley 6517B Electrometer/High Resistance Meter type. The samplewas irradiated for a few seconds under illumination through a microscopecondenser (numerical aperture of 0.55) with a 100 W halogen lightsource. An infrared filter was used for limiting the heating of thesample to a few degrees, which results in irradiation with a wide bandpower density of 10 W.cm⁻². The typical irradiation time of 10 scorresponds to the total number of photons used in about 0.30 minutesfor achieving self-assembly in solution by using a power density ofabout 0.07 W.cm⁻², which is more than required for generatingself-assembly. It was also discovered that a transition metal in theelectrode was necessary for ensuring more satisfactory interconnectionof the self-assembly. It is not possible to obtain stable and reliableself-assembly only between Au and Pt electrodes (with a Ti adhesionlayer). The self-assembly has a success rate of more than 90% betweentwo Ni and Fe electrodes. It was discovered that use of a gold deposit(Au) on the electrodes provides better long term stability of thesamples, and with this it is possible to overcome the problem of surfaceoxidation of the transition metals.

On the other hand, an effect initiating the growth of the self-assemblywas observed with a substrate of the transition metal type.

After the formation of the supramolecular structures, the samples wererinsed with chloroform, followed by intensive washing with acetone andethanol, and then finally dried with a stream of nitrogen.

Low temperature electric measurements were conducted with a cryostathaving a vacuum pump (P<10⁻⁶ mbar) or in a helium (He) flow systemlowering the temperature to 1.5K. The measurements of the electricproperties were conducted with an Agilent E5270B semiconductor parameteranalyzer (DC properties), and with an SRS 830 lock-in amplifier (ACproperties).

Differential conductance measurements were also conducted at 200K invacuo. A current with an intensity of a few tens of mA was observed in areproducible way with a 1V potential difference applied on differentsamples (FIG. 5).

The invention claimed is:
 1. A conducting material modified at a surfacewith an oriented bundle of electron conducting parallel nanowires offibrillar supramolecular species based on triarylamines of formula (I)below:

wherein: each of the groups -A¹- and -A²-, either identical ordifferent, designates a simple covalent bond or else a group —O—, —S—,—NH—, —NH(C═O)—, or —NR³—; each of the groups R¹, R² and R³, eitheridentical or different, represents: an aromatic group; or a hydrocarbonchain comprising from 4 to 30 carbon atoms, optionally halogenated andoptionally interrupted with one or more heteroatoms selected from N, Oor S; or a polyethylene glycol chain; and R is a terminating group. 2.An oriented bundle of electron conducting parallel nanowires offibrillar organic supramolecular species comprising triarylaminesfitting the formula (I) below:

wherein: each of the groups -A¹- and -A²-, either identical or differentdesignates a simple covalent bond or else a group —O—, —S—, —NH—,—NH(C═O)—, or —NR³—; each of the groups R¹, R² and R³, either identicalor different, represents: an aromatic group; or a hydrocarbon chaincomprising from 4 to 30 carbon atoms, optionally halogenated andoptionally interrupted with one or more heteroatoms selected from N, Oor S; or a polyethylene glycol chain; and R is a terminating group. 3.The oriented bundle of electron conducting fibrillar organicsupramolecular species according to claim 2, wherein each of the groupsR¹, R² and R³, represents aan aromatic benzyl group.
 4. The orientedbundle of electron conducting fibrillar organic supramolecular speciesaccording to claim 2, wherein each of the groups R¹, R² and R³, eitheridentical or different, represents a hydrocarbon chain comprising from 4to 30 carbon atoms, optionally halogenated and optionally interruptedwith one or more heteroatoms selected from N, O or S.
 5. The orientedbundle of electron conducting fibrillar organic supramolecular speciesaccording to claim 2, wherein R is CH₂-A and wherein R¹, R², and A haveone of the following meanings: R¹=R²=C₈H₁₇ (linear) and A=Cl; orR¹=R²=C₈H₁₇ (linear) and A=H; or R¹=R²=C₈H₁₇ (linear) and A=C₆H₁₃; orR¹=R²=benzyl and A=H; or R1=R2=benzyl and A=Cl.
 6. The conductingmaterial according to claim 1, wherein each of the groups R¹, R² and R³,represents an aromatic benzyl group.
 7. The conducting materialaccording to claim 1, wherein each of the groups R¹, R² and R³, eitheridentical or different, represents a hydrocarbon chain comprising from 4to 30 carbon atoms, optionally halogenated and optionally interruptedwith one or more heteroatoms selected from N, O or S.
 8. The conductingmaterial according to claim 1, R is CH₂-A and wherein R¹, R², and A haveone of the following meanings: R¹=R²=C₈H₁₇ (linear) and A=Cl; orR¹=R²=C₈H₁₇ (linear) and A=H; or R¹=R²=C₈H₁₇ (linear) and A=C₆H₁₃; orR¹=R²=benzyl and A=H; or R¹=R²=benzyl and A=Cl.
 9. The oriented bundleof electron conducting fibrillar organic supramolecular speciesaccording to claim 2, wherein each of the groups -A¹- and -A²- is agroup —O—.
 10. An oriented bundle of electron conducting fibrillarorganic supramolecular species according to claim 2, wherein each of thegroups R¹ and R², represents, independently: an aromatic benzyl group;or an alkyl group comprising from 6 to 18 carbon atoms.
 11. Thefibrillar organic supramolecular species according to claim 2, whereinthe triarylamines fit the formula (Ia) below:

wherein: each of the groups R¹and R², either identical or different,designates a benzyl group or a linear alkyl group, comprising from 6 to18 carbon atoms; A is a hydrogen group —H; a halogen group, or an alkylgroup.
 12. The oriented bundle of electron conducting fibrillar organicsupramolecular species according to claim 2, wherein each of the groupsR¹ and R², either identical or different, designates an aromatic benzylgroup or a linear alkyl group, comprising from 7 to 10 carbon atoms. 13.The oriented bundle of electron conducting fibrillar organicsupramolecular species according to claim 2, wherein R is a CH₂-A and Ais a hydrogen group —H; a halogen group; or an alkyl group.
 14. Theoriented bundle of electron conducting fibrillar organic supramolecularspecies according to claim 2, wherein each of the groups R¹ and R²independently represents: a linear alkyl group comprising from 7 to 10carbon atoms.
 15. The conducting material according to claim 1, whereineach of the groups -A¹- and -A²- is a group —O—.
 16. The conductingmaterial according to claim 1, wherein each of the groups R¹ and R²,represents, independently: an aromatic benzyl group; or an alkyl groupcomprising from 6 to 18 carbon atoms.
 17. The conducting materialaccording to claim 1, wherein the triarylamines fit the formula (Ia)below:

wherein: each of the groups R¹ and R², either identical or different,designates an aromatic benzyl group or a linear alkyl group, comprisingfrom 6 to 18 carbon atoms; A is a hydrogen group —H; a halogen group, oran alkyl group.
 18. The conducting material according to claim 1,wherein each of the groups R¹ and R², either identical or different,designates an aromatic benzyl group or a linear alkyl group, comprisingfrom 7 to 10 carbon atoms.
 19. The conducting material according toclaim 1, wherein R is CH₂-A and A is a hydrogen group —H; a halogengroup; or an alkyl group.
 20. The conducting material according to claim1, wherein each of the groups R¹ and R² independently represents alinear alkyl group.
 21. The conducting material according to claim 1,wherein said electron conducting fibrillar supramolecular species areohmic conductors.
 22. The oriented bundle of electron conductingfibrillar organic supramolecular species according to claim 2, whereinsaid electron conducting fibrillar supramolecular species are ohmicconductors.
 23. The oriented bundle of electron conducting fibrillarorganic supramolecular species according to claim 2, wherein each of thegroups -A¹- and -A²- designates a group —NH(C═O)—; and wherein each ofthe groups R¹, R² and R³, either identical or different, represents ahydrocarbon chain comprising from 4 to 30 carbon atoms, optionallyhalogenated and optionally interrupted with one or more heteroatomsselected from N, O or S.